This invention relates to improved methods and apparatus for dispensing chemicals for process operations. More specifically, the invention relates to methods and apparatus for photoresist delivery for processing semiconductor wafers.
The buildings and equipment required for processing high-value substrates such as electronic devices on semiconductor wafers are expensive. Such manufacturing processes are technologically challenging because of the high degree of precision needed for carrying out the processes and the requirement for a high level of cleanliness in the fabrication environment. Consequently, the investment cost of a modern operation for fabricating integrated circuits can cost over a billion dollars. The operation of facilities for fabrication of integrated circuits is also expensive because of utilities that are required such as high purity inert gas needed for purging equipment and other applications to support the clean environment.
Photolithography processes are essential in the production of most electronic devices. The nature of the photolithography process makes it particulate challenging. An important element of the photolithography process is the application of photoresist materials to substrates such as semiconductor wafers. In order to meet the demanding requirements for fabricating integrated circuits, the photoresist materials must be applied in very exact amounts. In addition, the photoresist materials need to be of extremely high purity so as to prevent contamination of the wafer surface with particles and other contaminants.
Some of the problems and potential solutions associated with the delivery of photoresist materials have been addressed before. U.S. Pat. No. 5,527,161 provides solutions to the problem of delivering precise amounts of photoresist materials to wafers; the patent also addresses the problem of providing particle free photoresist to the wafer. U.S. Pat. No. 4,950,124 describes a precision liquid dispenser using a displacement diaphragm pump and a hydraulic system for selectively deforming the diaphragm. A stepper motor and control system are described in U.S. Pat. No. 5,932,987 for controlling the volume of photoresist delivery to wafers.
Diaphragm pumps have gained wide acceptance for use in the delivery of photoresist to wafers. An example of a commercially available diaphragm pump suitable for such operations is made by the Millipore Corporation, the WCDS and WCDP P/R Pump models.
Although problems such as control of the delivery amount and purity of photoresist materials have been addressed, progress towards improving the efficiency of the photoresist delivery process has been weak or nonexistent. The standard control schemes for delivering photoresist with diaphragm pumps use a fixed time interval for controlling the pump refill step. The time interval for the refill steps are based on the viscosity of the chemical being delivered. Typically, the time interval for the refill step is set to 12 seconds for low viscosity chemicals and to 30 seconds for high viscosity chemicals. The standard methods use fixed time intervals even though the refill may be completed in less than the allocated fixed time. In other words, the standard methods and apparatus employ a very simple control scheme that may use more time than necessary to complete one of the steps required for photolithography.
As stated earlier, the investment cost and operating cost for electronic device fabrication are very high. It is important for the overall operation to operate as efficiently as possible so as to reduce the per unit cost for products and to generally improve the cost of ownership of the manufacturing operation. Even a small unnecessary waste, on a per wafer basis, can lead to significant additional operating expenses. In addition, the standard methods and apparatus for photoresist delivery are typically unsophisticated and matters such as failure detection and defect avoidance are unavailable.
Clearly, there is a need for improved methods and apparatus for photoresist delivery for applications such as processing semiconductor wafers for electronic device fabrication. There is a need for increased throughput and increased reliability for applications such as applying photoresist to semiconductor wafers during wafer processing operations. There is a need for improved operating efficiency for equipment used to deliver photoresist so that less time is wasted during wafer processing. Furthermore, there is a need for more sophisticated photoresist delivery equipment that can facilitate error detection and troubleshooting of the photoresist delivery equipment and process.
This invention seeks to provide methods and apparatus that can overcome deficiencies in known technologies used for dispensing chemicals such as for dispensing photoresist materials during semiconductor device fabrication.
One aspect of the present invention includes methods and apparatus for controlling a chemical dispense pump such as a chemical dispense pump used for dispensing photoresist materials onto wafers. The methods and apparatus includes actively monitoring the status of the dispense pump so that the dispense pump can be controlled in response to changes that occur during operation of the pump. According to one embodiment of the present invention, the refill step is actively monitored so as to determine the completion of the refill step so that the refill step can be terminated and the next step can be started with a reduction in unnecessary delay. A further embodiment includes methods and apparatus for measuring the pressure, more specifically, the level of vacuum applied to the chemical dispense pump for drawing the chemical into the pump for refill. The pressure is measured with resolutions that are sufficient to allow identification of the changes in the pressure that correspond to completion of the refill step.
In one embodiment of the present invention, the chemical dispense pump includes a diaphragm for moving the chemical. A pneumatic valve is arranged in communication with the diaphragm so as to drive the diaphragm. The apparatus includes a sensor for monitoring the position of the diaphragm. The sensor is connected with the pump. The apparatus further includes a controller; the controller is responsive to the sensor and provides control signals to the pneumatic valve so as to control dispensing the chemical.
As a further example, the sensor uses pressure to monitor the position of the diaphragm. The monitoring of the diaphragm""s position is determined by a pressure threshold. For example, the sensor can be arranged to measure pressure, more specifically the level of vacuum, between the diaphragm and the vacuum source. For example, the controller can be arranged to terminate the refill step when the pressure measurements indicate that the refill has been completed; consequently, the controller is able to start the next step upon completion of the refill step.
One example of a suitable sensor is a pressure sensor such as a semiconductor pressure sensor that converts pressure readings into voltage signals.
One example of a suitable controller is a microprocessor. In one embodiment, a microprocessor may be configured so as to be capable of controlling multiple chemical dispense pumps.
In one embodiment, the method includes monitoring the position of a diaphragm in a chemical dispensing pump such as Millipore""s Waferguard WCDS and WCDP. In a further embodiment, the position of the diaphragm is monitored by monitoring the pressure between the diaphragm and the vacuum source associated with controlling the diaphragm. The controller is arranged to terminate the refill step when the pressure measurements indicate that the refill has been completed; consequently, the controller is able to start the next step upon completion of the refill step. Optionally, the next that can be started without unnecessary delay.
Yet another aspect of the present invention includes methods and apparatus for monitoring a chemical dispense pump so that malfunctions of the chemical dispense pump can be detected. In one, embodiment the apparatus includes a pressure sensor arranged to measure pressure applied to valves and/or diaphragms used for moving and controlling the movement of the chemical being dispensed. The pressure sensor is connected with a controller responsive to the pressure sensor so that variations in the pressure with respect to time do not conform to predetermined variations, then an alarm is triggered and/or operation of the chemical dispense pump is suspended until the chemical dispense pump is checked for a possible malfunction.
It is to be understood that the invention is not limited in its application to the details of construction and to the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced and carried out in various ways. In addition, it is to be understood that the phraseology and terminology employed herein are for the purpose of description and should not be regarded as limiting.
As such, those skilled in the art will appreciate that the conception, upon which this disclosure is based, may readily be used as a basis for designing other structures, methods, and systems for carrying out aspects of the present invention. It is important, therefore, that the claims be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the present invention.
The above and still further features and advantages of the present invention will become apparent upon consideration of the following detailed descriptions of specific embodiments thereof, especially when taken in conjunction with the accompanying drawings.